Conventionally, a display apparatus such as a projector is connected to various devices via, for example, USB (Universal Serial Bus), and displays image data transmitted from these connected devices. Various devices connected to the display apparatus include a semiconductor memory device such as a flash memory device, a PC (Personal Computer), a digital still camera (to be referred to as a “digital camera” hereinafter), and the like.
A case will be explained first with reference to FIGS. 11A to 13C wherein a flash memory as a semiconductor memory device is connected to a projector as a display apparatus, and image data stored in that flash memory is displayed on the projector. FIG. 11A is a schematic view showing an overview when a flash memory 93 is connected to a conventional projector 91 to display an image. FIG. 11B is a schematic view showing details of a control panel 9101. FIG. 12 is a sequence chart showing the operation sequence executed when the flash memory 93 is connected to the projector 91 to display an image. FIGS. 13A to 13C are schematic views exemplifying images to be projected by the projector 91 onto a screen 92.
As shown in FIG. 11A, the projector 91 has the control panel 9101 and a USB connector 9102. As shown in FIG. 11B, the control panel 9101 has an up arrow button 9011, left arrow button 9012, down arrow button 9013, right arrow button 9014, enter button 9015, input button 9016, and power button 9017. The projector 91 accepts operation instructions from the user from various buttons on the control panel 9101. The USB connector 9102 receives the flash memory 93 having a USB connection terminal. This flash memory 93 stores image data to be displayed by the projector 91. By the user plugging the flash memory 93 into the USB connector 9102 and operating the control panel 9101, he or she can browse image data stored in the flash memory 93 as an image 921 on the screen 92.
The operation sequence among the user, flash memory 93, and projector 91 will be described below. Assume that the projector 91 is powered, and the flash memory 93 is not connected to the projector 91 in an advance state. As shown in FIG. 12, the operation sequence by the user, flash memory 93, and projector 91 mainly include steps S200 to S210 which are executed in turn. In step S200, the projector 91 displays a connection request window that requests the user to connect the flash memory 93 to the USB connector 9102 by projecting that window on the screen 92. The connection request window in step S200 displays a message that prompts the user to connect the flash memory 93 as a USB device, as shown in FIG. 13A.
In step S201, the user connects the flash memory 93 to the USB connector 9102. In step S202, a USB communication is established based on the USB standard between the projector 91 and flash memory 93 which are physically connected via the USB connector 102. In this case, the projector 91 recognizes the flash memory 93 as Mass Storage Class based on the USB standard.
In step S203, the projector 91 reads directory entry information stored in the flash memory 93. In step S204, the projector 91 displays a file selection window that prompts the user to select an image file to be displayed by projecting that window on the screen 92. The file selection window in step S204 is as shown in FIG. 13B, and is a window that displays a file name list of image files stored in the flash memory 93, and a cursor used to select them.
In step S205, the user who confirmed the aforementioned file selection window selects an image file to be displayed by operating the control panel 9101 and issues a display instruction to the projector 91. For example, in step S205 the user gives an instruction to move the cursor by pressing the up or down arrow button 9011 or 9013 on the control panel 9101, and issues a display instruction of an image file selected by the cursor by pressing the enter button 9015.
In step S206, the projector 91 reads data of the image file designated in step S205 from the flash memory 93. In step S207, the projector 91 displays an image based on the image file read in step S206 by projecting that image on the screen 92. As the image displayed in step S207, image data of a landscape or the like captured using a digital camera is stored in advance in the flash memory 93, as shown in FIG. 13C.
In step S208, the user issues a display end instruction to the projector 91 by operating the control panel 9101. More specifically, when the user presses the enter button 9015, a display end instruction is issued to the projector 91. Note that the operations for accepting selection of an image file by the user and displaying the selected image file can be repeated by repeating steps S204 to S208 bounded by the broken line in FIG. 12.
In step S209, the user removes the flash memory 93 from the USB connector 9102. In step S210, the projector 91 clears a display image projected onto the screen 92 (or overwrites the image by a predetermined image such as a menu window) due to removal of the flash memory 93 in step S209. For example, in step S210 the connection request window shown in FIG. 13A is overwritten on an image displayed in steps S204 to S208. As a result, the projector 91 can prompt the user to connect the next device. The user removes the flash memory 93 with the intention to end browsing of image files stored in the flash memory 93. Therefore, since the projector 91 clears an image displayed in steps S204 to S208, it can attain an image display operation according to the user's intention.
Note that patent reference 1 is known as a technique of clearing (overwriting) a display image by a predetermined image in step S210 above. Patent reference 1 discloses a technique for clearing a display image at the end of a communication and a technique for clearing a previous display image at the beginning of a communication.
A case will be exemplified below wherein another example of various devices to be connected is a digital camera. Note that a case will be exemplified below with reference to FIGS. 14A and 14B, and FIG. 15 wherein a digital camera is connected to a printer, and the printer outputs an image based on image data stored in that digital camera. As a typical example in this case, the CIPA DC-001-2003 standard (to be referred to as “PictBridge” hereinafter) is available. In a method of outputting an image using this PictBridge, even a user unskilled in operations of devices such as PCs can output an image using a printer by readily operating a digital camera. An image output operation using the PictBridge will be described below.
FIG. 14A is a schematic view showing an overview when a digital camera 94 is connected to a printer 96 to output an image. FIG. 14B is a block diagram showing the arrangement associated with a communication between the printer 96 and digital camera 94. FIG. 15 is a sequence chart showing the operation sequence when the digital camera 94 is connected to the printer 96 to output an image.
As shown in FIG. 14A, the printer 96 has a discharge port 9601 and USB connector 9602. The discharge port 9601 discharges a paper sheet 9603 after image formation. To the USB connector 9602, the digital camera 94 is connected via a USB cable 95. The digital camera 94 has a liquid crystal panel screen 9401, operation member 9402, and PictBridge button 9403. The liquid crystal panel screen 9401 displays a preview of an image or the like transferred via the PictBridge. The operation member 9402 accepts an image selection instruction from the user. The PictBridge button 9403 is a button which accepts an instruction to start PictBridge transfer from the user. An image based on image data stored in the digital camera 94 is output onto a paper sheet in the printer 96 in such a manner that an image output instruction is output to the printer 96 by an operation on the digital camera 94 side, and image data to be output is transmitted from the digital camera 94 to the printer 96.
The operation sequence among the user, digital camera 94, and printer 96 will be described below. As shown in FIG. 15, the operation sequence by the user, digital camera 94, and printer 96 mainly includes steps S500 to S509, which are executed in turn. In step S500, the user connects the digital camera 94 and printer 96 via the USB cable 95. In step S501, a USB communication is established based on the USB standard between the digital camera 94 and printer 96 which are physically connected via the USB cable 95. In this case, the printer 96 recognizes the digital camera 94 as a capture device of Imaging Class based on the USB standard.
In step S502, a PictBridge connection is established between the digital camera 94 and printer 96. More specifically, a connection is established in a PTP (Picture Transfer Protocol) layer, device information is exchanged, and so forth. Then, a communication state as a PictBridge sequence transits to an idle state, and the printer 96 waits for issuance of a print job by the digital camera 94.
In step S503, the user issues a print instruction via the PictBridge by operating the digital camera 94. More specifically, this print instruction in step S503 is issued when the user presses the PictBridge button 9403. In step S504, the digital camera 94 transmits a PictBridge print job to the printer 96 based on the print instruction in step S503, and the printer 96 starts the operation of that print job.
In step S505, the printer 96 requests the digital camera 94 to transmit file information to be printed in accordance with the print job in step S504, and acquires that file information. Likewise, in step S506 the printer 96 requests the digital camera 94 to transmit a file image (image data) to be printed in accordance with the print job in step S504, and acquires that file image.
In step S507, the printer 96 executes decoding, scaling, print processing, and the like of an image indicated by the file acquired in steps S505 and S506, and outputs the paper sheet 9603 after image formation from the discharge port 9601. In step S508, the printer 96 notifies the digital camera 94 of an idle state upon completion of the print job. Note that the operations for accepting selection of an image to be printed from the user, and printing out the selected image can be repeated by repeating steps S503 to S508 bounded by the broken line in FIG. 15.
In step S509, the user removes the USB cable 95 from the printer 96 or digital camera 94. Note that a device, which can control a communication session and logically disconnects a communication connection like the digital camera 94, often disconnects a communication like closing of a communication session in addition to a physical communication disconnection by, for example, removal of the USB cable 95. For example, when the battery remaining amount lowers during the aforementioned PictBridge sequence, the digital camera 94 side may execute control for disconnecting a USB communication so as to reduce consumption power.
A communication disconnection on the digital camera 94 side will be explained below by exemplifying the arrangement associated with a communication between the digital camera 94 and printer 96. As shown in FIG. 14B, a USB host controller 9604 on the printer 96 side is connected to a USB device controller 9407 on the digital camera 94 side via the USB cable 95. The USB cable 95 includes four signal lines, that is, a VBUS line 9501, D+line 9502, D− line 9503, and GND line 9504.
The D+ line 9502 and D− line 9503 are used to transmit differential signals required to make a USB data communication, and also indicate a device connection state by a voltage in a steady state. The D+ line 9502 and D− line 9503 are respectively pulled down by resistors 9606 and 9605 on the printer 96 side, and indicate a Low voltage when no USB cable is connected. Thus, the printer 96 recognizes a USB non-connection state. On the other hand, when the printer 96 and digital camera 94 are connected, the D+ line 9502 is pulled up by a resistor 9406 via a switch 9405 on the digital camera 94 side. Then, when the switch 9405 is in a connection state, the D+ line 9502 indicates a High voltage. As a result, the printer 96 recognizes a USB connection state.
A CPU 9404 controls the switch 9405 on the digital camera 94 side. Note that the CPU 9404 executes the following processing for the purpose of, for example, reducing consumption power of the digital camera 94. For example, in step S508 in which the PictBridge sequence transits to an idle state upon completion of the print job, the CPU 9404 controls the switch 9405 on the digital camera 94 side to stop to pull up the D+ line 9502. In this case, the D+ line 9502 indicates a Low voltage since it is pulled down on the printer 96 side. For this reason, the USB host controller 9604 recognizes a USB non-connection state and disconnects a USB communication, since this state is electrically equivalent to cable removal in association with the D+ line 9502. That is, the communication session between the digital camera 94 and printer 96 is closed by the control on the digital camera 94 side for the purpose of, for example, reducing consumption power.
When a communication disconnection is made on the digital camera 94 side, as described above, the user meets the same behavior as that when the USB cable 95 is removed at the end of the print processing of the printer 96. That is, the PictBridge sequence reaches the same state as that when the process reaches step S509.
Note that the PictBridge that assumes printing has been exemplified, but the PictBridge is applicable to a display on a display apparatus such as a projector or television. For example, when the digital camera 94 is connected to the projector 91 to display an image, as shown in FIG. 16, the PictBridge allows the projector 91 to project and display an image transmitted from the digital camera 94 by a simple operation on the digital camera 94 side. Like in the case in which the printer 96 and digital camera 94 are connected, when a communication is disconnected on the digital camera 94 side, the user meets the same behavior as that when the USB cable 95 is removed. That is, the projector 91 clears an image which was transmitted from the digital camera 94 and was displayed immediately before the communication disconnection by displaying, for example, the connection request window.
As a technique for disconnecting a USB communication from the device side, patent reference 2 is known. Patent reference 2 discloses a technique for disconnecting a communication by stopping to pull up a data line on the device side based on a disconnection instruction from the host side.    Patent Reference 1: Japanese Patent Laid-Open No. 7-123379    Patent Reference 2: Japanese Patent Laid-Open No. 2006-235993